4 THE MICROSCOPE. [January, 



each will be lightest, and the bright central spot will be some- 

 what dark. 



Distinctness of Outline. — In refraction images this depends 

 on the difference between the refractive power of a body and that 

 of the medium which surrounds it. The oil and air were very 

 distinct in outline, as each differed greatly in refractive power from 

 the medium which surrounds them, the oil being more refractive 

 than the mucilage, and the air less. 



Place a fragment of a cover-glass on a clean slide, and cover it. 

 The outline will be very distinct with the unaided eye. Use it as 

 object and employ the iS mm. (f in.) objective and high ocular. 

 Light with central light. The fragment will be outlined by a 

 dark band. Put a drop of water at the edge of the cover-glass. 

 It will run in and immerse the fragment. The outline will re- 

 main distinct, but the dark band will be somewhat narrower. 

 Remove the cover-glass, wipe it dry, and wipe the fragment and 

 slide dry also. Put a drop of 50% glycerin on the middle of 

 the slide and mount the fragment of cover-glass in that. The 

 dark contour will be much narrower than before. 



Draw a solid glass rod out to a fine thread. Mount one piece 

 in air. and the other in 50% glycerin. Put a cover-glass on each. 

 Emjulov the same optical arrangement as before. Examine the 

 one in air first. There will be seen a narrow, bright band, with 

 a wide dark band on each side. 



The one in glycerin will show a much wider bright central 

 band, with the dark borders correspondingly narrow. 



If the glass rod or any other object were mounted in a medium 

 of the same color and refractive power, it could not be distin- 

 guished from the medium. 



Study of Germinal Layers of Petromyzon. — Mr. S. Hatta 

 hardened the eggs and larvae of Petromyzon partly in Kleinen- 

 berg's picro-sulphuric acid, and partly in corrosive sublimate. 

 A few larvae were also killed in Flemming's solution. The sub- 

 limate specimens gave the best result. Picrocarmine was found 

 to be the best staining agent, as, being a nuclear stain and not af- 

 fecting the yolk granule, it made observation comparatively easy. 

 — Journal Coll. Sci. I?np. Univ. Japan, v {l8g2). 



Preparation of Vegetable Tissues. — Mr. A. Flatters, in 

 the Transactions of the Manchester Microscopical Society, 1891. 

 pp. 3S-47. gives detailed instructions in the use of the microtome 

 and the cutting of sections of vegetable tissues, the preparation 

 of leaf and flower-buds, the mounting of celloidinized sections, 

 and the staining of vegetable tissues with logwood and with 

 borax-carmine and iodine-green. Formulae are given for prepar- 

 ing Kleinenberg's hematoxylin, picrocarmine, borax-carmine, 

 and glycerine-jelly. 



